1. Field of the Invention
This invention relates to a pneumatic driven wrench, more particularly to a pneumatic driven wrench with a mis-switching prevention capability.
2. Description of the Related Art
FIGS. 1 and 2 illustrate a conventional pneumatic driven wrench 1 including: an outer housing 10, an inner housing 11 that has first and second parts 111, 123 which are connected to each other and which respectively define an inlet channel 112 and a middle channel 124 for receiving a compressed air therein; a cylinder 12 that extends from the second part 123 and that defines a rotor chamber 120, a first fluid passage 126, and a second fluid passage (not shown), the first fluid passage 126 and the second fluid passage being in fluid communication with the rotor chamber 120; an annular valve 13 that is sleeved rotatably on the second part 123; a rotor 122 that is mounted rotatably in the rotor chamber 120 and that is driven to rotate by the compressed air flowing from the inlet channel 112 through the middle channel 124 and into the rotor chamber 120; an inlet valve 151 that is mounted in the second part 123 and that is disposed between the inlet channel 112 and the middle channel 124 for controlling fluid communication between the inlet channel 112 and the middle channel 124; a spring-biased trigger switch 15 pivoted to the outer housing 10 and connected to the inlet valve 151 for opening and closing the inlet valve 151; and an annular valve-rotating member 14 that is rotatably sleeved on the outer housing 10 and that is coupled to the annular valve 13 for driving rotation of the annular valve 13 between a first angular position (see FIG. 2), in which the annular valve 13 permits fluid communication between the middle channel 124 and the first fluid passage 126 while preventing fluid communication between the middle channel 124 and the second fluid passage, thereby permitting rotation of the rotor 122 relative to the cylinder 12 in a first rotational direction, and a second angular position (not shown), in which the annular valve 13 prevents fluid communication between the middle channel 124 and the first fluid passage 126 while permitting fluid communication between the middle channel 124 and the second fluid passage, thereby permitting rotation of the rotor 122 relative to the cylinder 12 in a second rotational direction opposite to the first rotational direction.
The conventional pneumatic driven wrench 1 is disadvantageous in that the annular valve-rotating member 14 can be accidentally rotated by a user to cause undesired rotation of the annular valve 13 between the first and second angular positions and thus undesired switching of the rotational directions of the rotor 122 while the rotor 122 is rotating in one of the first and second rotational directions, which can result in damage to the rotor 122 and a decrease in the service life of the pneumatic driven wrench 1.